The objectives of this project are to examine the molluscan portion of the life cycle of Schistosoma mansoni in the intermediate snail host, Biomphalaria glabrata, with the intention of acquiring knowledge which might make it possible to interfere with the transmission of schistosomiasis to man via the molluscan vector. Goals set for the coming year include: 1. the study of the ultrastructure of capsules formed around sporocysts using SEM and TEM to determine how snail cells attach to and kill sporocysts; 2. investigation of the chemical characteristics of the sporocyst tegument to determine factors responsible for the sporocyst's ability to remain undetected by host cells; 3. culture and identification of cells capable of encapsulation from explants of snail head-foot and mantle; 4. comparison of the viability of sporocysts in the plasma of refractory vs. susceptible snail strains to determine whether sporocyst death due to nutritional deficiencies or soluble toxic factors may precede encapsulation in refractory snails.